JP5890730B2 - Welding method - Google Patents

Description

  The present invention relates to a gas shielded arc welding method used, for example, for butt welding of steel plates.

  In recent years, repair and reinforcement have been carried out in accordance with damage to existing bridges due to an increase in traffic volume and vehicle weight. In order to cope with the increase in traffic and vehicle weight, functions such as widening (increasing the number of lanes) and upgrading from second-class bridges (for 14t cars) to first-class bridges (for 20t cars) have been attempted. ing.

  In general, since the bridge cannot be taken back to the factory, the various constructions described above are performed at the bridge installation location. When stopping traffic in connection with these constructions, in order to reduce the influence on the local community and economy, it is necessary to carry out only at night when the traffic volume is relatively low, or at least one lane should be able to travel. As a result, problems such as time constraints on construction work, ensuring worker safety, and effects on surrounding residents (for example, noise) have become prominent.

  Therefore, there is an increasing demand for construction in service without stopping traffic. When construction is performed under such a service, for example, as a method for joining steel plates, there are welding joining and high-strength bolt joining. Conventionally, high-strength bolt joining has been mainly used for bridges. The reason for this is that it has been thought that the reliability of welded joints cannot be guaranteed when welding is performed under such conditions because the bridges in service are subject to vibration and displacement of the groove due to traveling vehicles. is there.

  FIG. 7 shows a state in which the vehicle is traveling on the steel floor slab bridge. The bridge portion shown in FIG. 7 includes a left lane block 11 and right lane blocks 12 and 13. The left lane block 11 and the right lane blocks 12 and 13 are welded to each other, and the right lane blocks 12 and 13 are welded to each other. Here, when the vehicle 15 travels on the left lane block 11, vibration and groove displacement occur in each welded portion.

  However, even in high-strength bolted joints, the mechanical performance of the joint when constructed under load and vibration is not always clear. Further, when comparing the welding joint and the high-strength bolt joint, as is apparent from the respective joining methods, the welding joint is structurally simpler, has a higher degree of freedom, and has superior joining efficiency. Therefore, since the effect is great if welding under service is possible, for example, Patent Document 1 proposes a welding method under service.

JP-A-6-170539

  The welding method proposed in Patent Document 1 is premised on welding work such as covered arc welding using a welding rod. When such welding construction is applied to, for example, welding of a steel floor slab as shown in FIG. 7, a large number of welding rods are required to form a continuous welded portion over a long distance. Inefficiency. In addition, since the operation is temporarily interrupted every time the welding rod is updated, there is a high possibility that a defect occurs in the welded portion due to the discontinuity of the operation.

  On the other hand, gas shielded arc welding, in which welding is performed by shielding arc points with gas, is known as an efficient welding method. In the gas shielded arc welding, a welding material such as a wire that is not substantially limited to one welding operation distance is used instead of a welding electrode such as a covered arc welding rod having a short one welding operation distance. Thereby, it becomes possible to form the welding part which continues over a long distance without work interruption.

  However, because of the difference in the welding mechanism between the covering arc welding and the gas shielded arc welding, even if the chemical compositions of the two welding materials are the same, the characteristics of the formed welded portion are not the same. Therefore, the welding method proposed in Patent Document 1 cannot be directly applied to gas shielded arc welding under service.

  In view of the above, an object of the present invention is to enable gas shielded arc welding in service and thereby to form a welded portion continuous over a long distance with high strength and efficiency.

  In order to achieve the above object, a welding method according to the present invention is a method of performing welding under variable stress, and measures the root gap opening displacement before the start of welding and corresponds to the measured root gap opening displacement. The welding material having the Mn / S ratio and the Mn / Si ratio thus selected is selected from the materials for gas shielded arc welding having a welding distance one time longer than that of the coated arc welding rod.

  According to the welding method of the present invention, the Mn / S ratio and the Mn / Si ratio in the welding material are determined based on the measurement result of the root gap opening displacement before the start of welding. Welding materials with good crack resistance can be selected. Therefore, since welding under gas shield arc welding is possible, it is possible to efficiently form a welded portion continuous over a long distance with high strength.

  In the welding method according to the present invention, the root gap opening displacement at the time of welding is measured, and when the measured root gap opening displacement exceeds the allowable value assumed in the selection of the welding material, the time when the allowable value is exceeded. You may confirm the quality of the welding part formed in this.

  In this way, even if the root gap opening displacement exceeds the allowable value and quality degradation occurs in the welded part during welding on site, the degraded part is identified and inspected and repaired (if necessary). It can be done easily.

  In the welding method according to the present invention, the welding material may be selected based on a root gap.

  In this way, in addition to the measurement result of the root gap opening displacement before the start of welding, it is possible to select a more appropriate welding material in consideration of the root gap itself.

  According to the present invention, it is possible to perform gas shielded arc welding under service, and thereby, a welded portion continuous over a long distance can be efficiently formed with high strength.

FIG. 1 shows the chemical composition of a welding rod that was the subject of the transbarestrain test by the present applicants. FIG. 2 shows the relationship between the Mn / S ratio and Mn / Si ratio and the cracking resistance of the welding rod, which has been found by the transbarestrain test by the present applicants. FIGS. 3A and 3B show a test conducted by the inventors of the present application to examine the applicability of in-service gas shield arc welding. FIG. 4 shows the chemical composition of the welding material used in the welding test shown in FIGS. 3 (a) and 3 (b). FIG. 5 shows the result of the welding test shown in FIGS. 3A and 3B using the welding material shown in FIG. FIG. 6 shows a flow of the welding method according to the embodiment. FIG. 7 shows a state in which the vehicle is traveling on the steel floor slab bridge.

(Premise of the present invention)
The applicants of the present application are resistant to cracking when a strain is applied to a plurality of welding rods (φ4 mm) having various chemical compositions (unit: wt%) as shown in FIG. Have been investigating. As a result, it was confirmed that the effect of the Mn / Si ratio and the Mn / S ratio on the welding rod on the crack was great.

  Specifically, as shown in FIG. 2, it was confirmed that the resistance to cracking under a variable load was improved as the Mn / S ratio and the Mn / Si ratio in the welding rod were increased.

  Therefore, the inventors of the present application have proposed a welding material having a different Mn / S ratio and Mn / Si ratio (specifically, a gas shield such as a wire having a longer welding distance than a welding rod such as a coated arc welding rod). In order to investigate the applicability of in-service gas shielded arc welding using a material for arc welding, a welding test was performed while changing the root gap (G) and the root gap opening displacement (Δδ) in various ways. .

  Specifically, as shown in FIG. 3A, the base materials 1 and 2 having a thickness T are abutted at the root gap G, and as shown in FIG. A backing 3 was provided on the bottom, and gas shield arc welding was performed using carbon dioxide gas to form a weld 4 and the base materials 1 and 2 were joined.

  Further, as the welding material, the welding material A (Mn / S ratio = 160, Mn / Si ratio = 2.98) and the welding material B (Mn / S ratio = 130, Mn / Si) having the chemical composition shown in FIG. Ratio = 26) was used.

  Further, as the base materials 1 and 2, a rolled steel material SM490A having a thickness T of 16 mm was used. In addition, the route gap G is set in two ways of 4 mm and 10 mm, and the route gap opening displacement Δδ (before welding) is set in three ways of 0.2 mm, 0.3 mm, and 0.4 mm in each route gap G value. Then, a welding test was conducted. For the root gap opening displacement Δδ, by displacing the base materials 1 and 2 using a servo mechanism that holds the opposite side of the groove side of the base materials 1 and 2, and measuring the displacement using a displacement meter, The predetermined value was set as described above. In this welding test, the frequency of the root gap opening displacement Δδ was set to 3.7 Hz, which is close to the frequency of vibration induced by the traveling vehicle.

  FIG. 5 shows the result of a welding test using the above-described welding material. Here, the result determination was performed by examining whether or not a defect such as a crack or a blow hole (BH) occurred in the welded portion by ultrasonic flaw detection inspection (UT) and radiation transmission inspection (RT). In FIG. 5, the case where there is no defect is indicated by ◯, and the case where there is a defect is indicated by ×. Moreover, the edge crack which can be prevented by installation of an end tab was not included in the defect.

  As shown in FIG. 5, when the welding material A is used, if the root gap G is 4 mm which is a general value, a defect occurs even if the root gap opening displacement Δδ is 0.4 mm which is relatively large. No results were obtained. Further, even when the root gap G was set to 10 mm in consideration of a sufficient margin in the construction, if the root gap opening displacement Δδ was 0.2 mm, welding was possible without using the welding material A.

  On the other hand, when the welding material B is used, if the root gap G is 4 mm, no defect occurs even if the root gap opening displacement Δδ is 0.2 mm. However, if the root gap G is 10 mm, the root gap opening Defects occurred when the displacement Δδ was 0.2 mm.

  From the results of the welding test described above, the present inventors measured the root gap opening displacement before the start of welding, and coated the welding material having a Mn / S ratio and a Mn / Si ratio corresponding to the measurement results. It has been found that gas shield arc welding under variable stress becomes possible by selecting and using a gas shield arc welding material that has a longer welding distance than an arc welding rod. Also, the root gap opening displacement is measured during actual welding work on site, and when the measured root gap opening displacement exceeds the allowable value assumed when selecting the welding material, it is formed at the time when the allowable value is exceeded. By checking the quality of the welded part, it was found that the deteriorated part can be identified and easily inspected and repaired (if necessary). Furthermore, when selecting a welding material, it has been found that a more appropriate welding material can be selected by considering the route gap itself in addition to the measured value of the root gap opening displacement before the start of welding.

(Embodiment)
Hereinafter, a welding method according to an embodiment of the present invention will be described with reference to the drawings. The welding method according to the present embodiment is a gas shielded arc welding method under service (that is, under fluctuating stress) based on the knowledge described in the above-mentioned “premise of the present invention”.

  FIG. 6 is a flowchart of the welding method according to the present embodiment.

  First, in step S1, the steel type, shape, dimensions, etc. of the joint to be welded are confirmed based on, for example, a construction plan.

  Next, in step S2, the root gap opening displacement Δδ (before welding) at the time of service is measured for the joint confirmed in step S1.

  Next, in step S3, a welding material having a Mn / S ratio and a Mn / Si ratio that can correspond to the root gap opening displacement Δδ measured in step S2 (the welding operation is performed once more than a welding rod such as a coated arc welding rod) Select a gas shielded arc welding material such as a long distance wire. Specifically, based on the measurement result of the root gap opening displacement Δδ, the maximum value (allowable value) of Δδ is set, and the Mn / S ratio and Mn / Si ratio exhibiting sufficient crack resistance even with the allowable value. Select the welding material.

  For example, when the route gap G is determined to be 4 mm or less in a construction plan or the like, if the allowable value of the route gap opening displacement Δδ is 0.2 mm, any of the above-described welding materials A and B can be used. On the other hand, if the allowable value of the root gap opening displacement Δδ is 0.4 mm, the above-mentioned welding material A can be used. Further, when the allowable value of the root gap opening displacement Δδ exceeds 0.4 mm, a welding material that exhibits sufficient cracking resistance even at the allowable value, that is, the Mn / S ratio and the Mn / Si ratio than the welding material A described above. It is necessary to select and use a welding material having a large size.

  In addition, when the root gap G can be arbitrarily set, the welding material is selected in consideration of the root gap G. For example, when the allowable value of the root gap opening displacement Δδ is 0.2 mm and the root gap G is set to 4 mm, both of the above-mentioned welding materials A and B can be used, while the root gap opening displacement In the case where the allowable value of Δδ is also 0.2 mm, when the root gap G is set to 10 mm, the above-described welding material A can be used.

  Next, in step S4, gas shield arc welding is performed on the joint to be welded using the welding material selected in step S3.

  As described above, according to the present embodiment, the Mn / S ratio and the Mn / Si ratio in the welding material are determined based on the measurement result of the root gap opening displacement Δδ before the start of welding. It is possible to select a welding material having sufficient crack resistance under variable stress. Therefore, since welding under gas shield arc welding is possible, it is possible to efficiently form a welded portion continuous over a long distance with high strength.

  In this embodiment, when the gas shield arc welding is performed in step S4, the root gap opening displacement Δδ at the time of welding is measured, and the measured value exceeds the allowable value assumed in the selection of the welding material. The quality of the weld formed at the time when the allowable value is exceeded may be checked. In this way, even when the root gap opening displacement Δδ exceeds the allowable value during the welding operation in the field and the quality deteriorates in the welded portion, it is possible to easily identify and reinforce the deteriorated portion. it can.

  In the present embodiment, for example, according to the measurement result of the root gap opening displacement Δδ in step S2, the allowable value of Δδ exceeds 0.4 mm. However, as a selectable welding material, the allowable value of Δδ is When there is only material of 0.4 mm or less, it may be as follows. That is, for example, the route gap opening displacement Δδ is measured again in step S2 after reducing the route gap opening displacement Δδ by, for example, installing a restraint plate or restricting traffic. Thereafter, until the allowable value of Δδ becomes equal to or less than 0.4 mm, the above-described constraint conditions and regulation contents are made stricter sequentially. Here, when the route gap G is variable, the route gap G may be reduced.

  Moreover, in this embodiment, the kind of joint used as welding object, the kind of steel materials used as a joint, thickness, etc. are not specifically limited. For example, a steel material having a strength comparable to or less than that of SM490A, such as SM400A, SM400B, SM490B, SM490YA, and SM490YB of JIS G 3106 may be used for butt welding with a thickness of 16 mm or less.

  In the present embodiment, the Mn / S ratio and the Mn / Si ratio in the welding material used for gas shield arc welding are not particularly limited. However, the higher the Mn / S ratio and the Mn / Si ratio, the better the resistance to cracking when strain is applied, but as the amount of Mn contained in the welding material increases, the cost required for the material increases. In addition, the viscosity of the droplets during welding becomes high, and it becomes difficult to ensure the uniformity of the welded portion. Therefore, it is advantageous in terms of cost, workability, and the like to use a welding material having a low Mn / S ratio and Mn / Si ratio within a range that can correspond to the measurement result of the root gap opening displacement Δδ before the start of welding. Further, according to the investigation by the applicants of the present application using a welding rod having the chemical composition shown in FIG. 1, it is preferable to reduce the amounts of C, Si, P, and S contained in the welding material as much as possible.

  In the present embodiment, the type of shield gas used for gas shield arc welding is not particularly limited. However, as the content of the inert gas (for example, Ar) in the shield gas is higher, the effect of reducing spatter can be obtained. On the other hand, as the content of the inert gas increases, the cost required for the shield gas increases. End up.

  By the way, when performing multi-layer welding in a welding operation under service, the crack is most likely to occur in the first layer, while the root gap opening displacement Δδ greatly decreases in the second and subsequent layers. Therefore, when performing multilayer welding, you may perform the gas shield arc welding of this embodiment about all the layers, or you may perform the gas shield arc welding of this embodiment only about the first layer, for example. In other words, for the second and subsequent layers, a welding material having a smaller Mn / S ratio and Mn / Si ratio may be used.

  In addition, the application target of the welding method of the present embodiment is not limited to a bridge that is highly required for in-service welding. For example, other steel structures that are subject to fluctuating stress caused by the external environment, such as a steel tower or the like The effect by applying the welding method of this embodiment is great also in offshore structures and the like.

  The present invention is useful as a gas shielded arc welding method used, for example, for butt welding of steel plates.

DESCRIPTION OF SYMBOLS 1 Base material 2 Base material 3 Backing 4 Welding part 11 Left lane block 12 Right lane block 13 Right lane block 15 Vehicle

Claims (2)

A method of welding under variable stress,
Measure the root gap opening displacement before the welding start in the root gap 4 mm, gas the measured root gap opening Mn / S ratio corresponding to displacement and Mn / Si ratio is 160 or more 2.98 or more welding material A process of selecting from shield arc welding materials ;
When the root gap opening displacement at the time of welding with the gas shielded arc welding material in service is measured, and the measured root gap opening displacement exceeds the allowable value 0.4 mm assumed in the selection of the welding material, A process of identifying a weld formed at a time exceeding the allowable value as a deteriorated part;
And a step of inspecting or repairing the deteriorated portion . A method of welding under variable stress,
The root gap opening displacement before the start of welding at the root gap of 10 mm is measured, and a welding material having a Mn / S ratio of 160 or more and a Mn / Si ratio of 2.98 or more corresponding to the measured root gap opening displacement is gas shielded. A process of selecting from arc welding materials;
Measure the root gap opening displacement at the time of welding with the gas shielded arc welding material under service, and the measured root gap opening displacement exceeds the allowable value 0.2 mm assumed in the selection of the welding material, A process of identifying a weld formed at a time exceeding the allowable value as a deteriorated part;
A step of inspecting or repairing the deteriorated portion.
A welding method characterized by the above.

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